A finite element(FE)model of temperature field of permafrost subgrade is constructed with ABAQUS and the secondary development platform. Then, the temperature fields of narrow subgrade and wide subgrade are compared and analyzed with the FE model. Furthermore, the change rules of melting depth of wide subgrade are studied. The results demonstrate that the temperatures of subgrades with different widths all change periodically over time, but the mean annual temperature rises. With the increase in the width, the temperature rises but the rate decreases gradually. The melting depth at the centerline shows a three-stage rising trend when the width increases, and the melting depth at the shoulder increases linearly. The melting depth at the basal slope rises with the increase in the width, but the variation is very small. Increasing the height of wide subgrade is helpful to protect permafrost; however, the effect will reduce after the height reaches a certain value.